1. Field of the Invention
The present invention generally relates to subterranean drilling equipment. More particularly, the present invention relates to a system and method for detecting roller bit wear in a roller-cutter drill through preventing the rotation of the roller bit having a worn roller bit bearing, and detecting the presence of the non-rotating roller bit is detectable such that the drilling operation can be stopped prior to roller drill bit failure.
2. Description of the Related Art
In rotary-cutter type subterranean drills, rotary drill bits are a commonly used type of drill bit, especially in the oil and gas well drilling industry, because the rotary drill bit offers a satisfactory rate of penetration with a significant operational life in drilling most commonly encountered formations. Roller-cutter drill bits include a bit body having a threaded pin at its upper end adapted to be detachably secured to a drill string suspended from a drill rig, and a plurality of depending legs, typically three such legs, at the lower end of the body. The drill bit further includes a plurality of conical or spherical roller-cutters having cutting elements thereon, with one roller-cutter on each leg, and each leg typically includes a bearing for rotatably mounting each roller-cutter thereon.
Sealed bearing type roller-cutter bits further have a lubrication system including a reservoir holding a supply of lubricant. A passage in the bit body extends from the reservoir to the bearing to allow flow of lubricant to the bearing. A seal is disposed between the roller cutter and the bearing journal that holds lubricant in the bit. A diaphragm at the reservoir provides pressure compensation between the lubricant and the drilling fluid in the annulus between the bit and the well bore.
In use, roller cutter drill bits are rotated in the well bore on the end of a drill string that applies a relatively high downward force onto the drill bit. As the bits are rotated, the conical roller cutters rotate on the bearing journals thereby bringing the cutting elements on the roller cutters into engagement with the substrate at the bottom of the well bore. The cutting elements drill through the substrate at the well bore bottom by applying high point loads to the substrate to thereby cause the substrate to crack or fracture from the compression. A drilling fluid, commonly called drilling mud, passes under pressure from the surface through the drill string to the drill bit, and is ejected from one or more nozzles adjacent the roller-cutters and the drilling fluid is then forced back up the well bore to the surface.
For cost-effective drilling, a worn drill bit needs to be replaced due to the reduced rate of drilling penetration for the worn bit. At a certain point, the cost of replacing the old drilling bit with a new bit becomes equal to the cost of the drilling inefficiency, or in other words, the cost of the new bit plus the cost of rig time in moving the drill string in and out of the well bore is less then cost of operating the worn bit. Unfortunately, once a drill bit is positioned in a well bore, gathering reliable information regarding the operating condition, performance and remaining useful life of the drill bit becomes difficult. Typically, the decision by a drilling rig operator to replace a drill bit is a subjective one, based upon experience and general empirical data showing the performance of similar drill bits in drilling similar substrate formations. However, the rig operator""s decision as to when to replace a drill bit is often not the most cost effective because of the many factors affecting drilling performance beyond the condition and performance of the bit itself.
In the worst case, the drilling rig operator may unknowingly run the drill bit until failure. Bit failure may also result from an improper application of the bit, such as by excessive weight on the drill bit from the drilling string, excessive rotational speed, and drilling with the wrong type of bit for the substrate being drilled, or even from a defect in the drill bit itself. Bit failures typically occur in one of two modes: (1) breakage of the cutting elements, or (2) bearing failure. The first mode of failure is more common, and the second mode is more serious.
In the first mode, pieces of the cutting elements, which are typically either steel teeth or tungsten carbide inserts, are broken from the roller cutters. This breakage does not normally stop the drilling action but it does significantly reduce the rate of drilling penetration, and the broken pieces are mostly carried away from the well bore bottom by the circulating drilling fluid thereby leaving the well bore bottom clean for a replacement bit.
The second mode of failure can occur if the bit is continued to be used with a worn bearing assembly as the assembly will no longer be able to hold the roller cutter on the bearing journal, and consequently, the roller cutter will fall from the bit when the drill string is pulled from the well bore. A lost roller cutter can be retrieved from the well bore bottom only by a time-consuming and expensive xe2x80x9cfishingxe2x80x9d operation in which a special retrieval tool is tripped in and out of the well bore to retrieve the broken cutter and any pieces.
In sealed bearing roller cutter bits, bearing failure is often the result of a seal failure that causes lubricant to flow out of the drill bit and drilling fluid, which contains abrasive particles, to flow into the bearing. Although less common, diaphragm failure has the same result as seal failure. In any event, bearing failure is almost always preceded by, or at least accompanied by, a loss of lubricant and uneven rotation or vibration of the roller bit.
Numerous bearing failure indicator systems have been proposed for inclusion in drill bits so as to give the drilling rig operator a signal predicting bearing failure. One such system involves measurement and interpretation of certain drilling parameters at the drill rig, such as drill string torque, weight on bit, and rate of penetration, to predict drill bit bearing failure. In practice this system has proved to be unreliable, likely due to the large number of variables other than bit performance, such as the type of substrate formation and the pressure and flow rate of the drilling fluid, which affect the drilling parameters that are measured at the drill rig.
Another system, involves a marker fluid, such as a radioactive material in the bearing lubricant, which is released into the drilling fluid upon bearing failure. The released marker fluid is detected at the drill rig when the drilling fluid is circulated back up to the surface. While this method does detect the loss of lubricant in a sealed bearing drill bit that precedes, or at least accompanies, the failure of the bearings of the roller bit, and thus is a reliable indication of bit failure, the system has several shortcomings. In addition to the difficulties present in handling radioactive materials, a major shortcoming is that a significant amount of marker fluid must be released into the relatively large volume of drilling fluid or else become so diluted as to be undetectable.
Therefore, it would be advantageous to provide a system and method to reliably detect the wear of a roller bit prior to catastrophic failure of the roller bit such that the roller bit, the roller cutters, or pieces thereof require extrication from the well bore. Such method should be simple in implementation and not require separate elaborate equipment to be used at the drill rig or on the drill bit. Further, such system and method should be easily redeployed once the roller bit or bits have been changed. It is thus to the provision of such an improved method for detecting roller bit bearing wear that the present invention is primarily directed.
The present invention is a system and method for detecting the wear of a roller bit bearing holding a roller element on a roller drill bit body. The roller element has a plurality of cuffing elements and is rotatably attached to the roller drill bit body at the bearing, and rotation of the roller element causes the cutting elements to drill into the substrate. The invention uses a rotation impeder in between the roller element and roller drill bit body that selectively impedes the rotation of the roller element upon uneven rotation of the roller element. The uneven rotation, or xe2x80x9cwobble,xe2x80x9d of the roller element is typically caused by the bearing beginning to fail and is an excellent indicator of an impending bearing failure. The rotation impeder can be housed in either the roller drill bit body or the roller element.
In one embodiment, the roller drill bit body includes a drilling fluid passage and outlet therein and the rotation impeder is positioned in the fluid outlet to prevent drilling fluid from flowing through the passage and out of the outlet. When the rotation impeder deploys upon uneven rotation of the roller element to impede the rotation of the roller element, the rotation impeder is also removed from the fluid outlet whereby drilling fluid flows from the drilling fluid outlet. In such embodiment, both the cessation of roller element rotation and drop in drilling fluid pressure due to the opening of the drilling fluid outlet can be detected at the surface to indicate an impending roller bearing failure.
The rotation impeder, in one embodiment, is a selectively extendable detent held in the roller drill bit body and is selectively extended from the roller drill bit body and into a recess of the roller element to thereby cease rotation of the roller element. In another embodiment, the roller drill bit body includes a roller drill bit body recess therein that faces the roller element when rotatably attached to the roller bit bearing, and the roller element includes a roller bit element recess therein which interfaces the roller drill bit body recess. In such embodiment, the rotation impeder can be a ball bearing and a spring in the roller drill bit body wherein upon uneven rotation of the roller element, the ball bearing is ejected into the roller element recess and the ball bearing becomes lodged between the roller element recess and the roller drill bit body recess to thereby cease rotation of the roller element. Alternately, the rotation impeder can be a wedge selectively fitted in the roller drill bit body, wherein upon uneven rotation of the roller element, the wedge is ejected into the roller element recess and the wedge becomes lodged between the roller element recess and the roller drill bit body to thereby cease rotation of the roller element.
The present invention further provides a method for detecting the wear of a roller bit bearing of a roller drill bit body having a roller element including a plurality of cutting elements rotatably attached thereto at the bearing, and a rotation impeder that selectively impedes rotation of the roller element is in between the roller element and roller drill bit body. The method includes the steps of rotating the at least one roller element, and upon uneven rotation of the at least one roller element, impeding the rotation of the at least one roller element with the rotation impeder, and detecting the cessation of the rotation of the at least one roller element.
If the roller drill bit body includes a drilling fluid passage and outlet therein with the rotation impeder positioned in the fluid outlet to prevent drilling fluid from flowing through the passage, the method further includes the steps of, upon uneven rotation of the roller element causing the rotation impeder to impede the rotation of the roller element, removing the rotation impeder from the fluid outlet whereby drilling fluid flows from the drilling fluid passage, and detecting the drop in drilling fluid pressure that occurs from the open fluid outlet.
It the roller element includes a recess that is placed in between the roller element and roller drill bit body with a detent held in the roller drill bit body, the step of impeding the rotation of the at least one roller element with the rotation impeder is selectively extending the rotation impeder from the roller drill bit body into the recess to thereby cease rotation of the roller element. If the roller drill bit body includes a roller drill bit body recess therein facing the roller element and the roller element includes a roller element recess therein which interfaces the roller drill bit body recess, and the rotation impeder is comprised of a ball bearing and a spring in the roller drill bit body, the step of impeding the rotation of the at least one roller element with the rotation impeder is impeding the rotation of the at least one roller element through ejecting the ball bearing into the roller element recess and the ball bearing becoming lodged between the roller element recess and the roller drill bit body recess to thereby cease rotation of the roller element. Alternately, when the roller drill bit body and roller element include a roller drill bit body recess and a roller element recess respectively, and the rotation impeder is a wedge selectively fitted in the roller drill bit body, the step of impeding the rotation of the at least one roller element with the rotation impeder is impeding the rotation of the at least one roller element through ejecting the wedge into the roller element recess and the wedge becoming lodged between the roller element recess and the roller drill bit body to thereby cease rotation of the roller element.
The present invention therefore provides a simple and inexpensive system and method to detect roller bit wear during the drilling operation using cessation of the rotation of one or more roller elements as an indication of the condition of the roller bit bearing. The invention can also use a second method of detecting possible bearing failure by also opening an additional outlet of drilling fluid to cause a greater volume than normal of drilling fluid to flow during operation of the roller drill bit, and the resultant drop in the drilling fluid pressure can be detected. Both the frequency of roller bit rotation and drilling fluid pressure can be monitored in extant drilling equipment, and thus the present invention can be implemented in an existing drill rig without the need for installation of additional specific monitoring equipment.
Further, the present invention does not require significant effort to redeploy the detection system because the rotation impeder can easily be reset or replaced once a new roller element or component, such as a bearing, is replaced on the roller-cutter drill bit. If embodied with the rotation impeder held in the drilling fluid outlet, the rotation impeder is also easily replaced into a drilling fluid outlet once the new roller element or components are replaced on the roller-cutter drill bit.
Other objects, features, and advantages of the present invention will become apparent after review of the hereinafter set forth Brief Description of the Drawings, Detailed Description of the Invention, and the claims.